Automatic video format identification system

ABSTRACT

A video format identification system includes a master clock circuit which provides timing and counting signals, a synchronization activity detector operatively coupled to the master clock circuit, and a synchronization width qualifier configured to filter out noise or reference burst signals from showing up as sync signals. The system also includes a synchronization detector which regulates the rate of the incoming sync signal, a color burst sampler providing a window for sampling a reference color burst after the sync signal has occurred, and a color burst detector which looks for at least three transitions from a burst signal before it qualifies the as an appropriate reference color burst. A format sample timer generates sample clock signals. A format sample counter produces “take format” signals which are utilized by a set of format counter. The system further includes a video format identifier which enables a particular video format to be directed to a respective video connector.

FIELD OF THE INVENTION

The present invention relates to communication systems. Morespecifically, the invention relates to an automatic video formatidentification system.

BACKGROUND

Transmission cables are used to convey electronic signals from a sourcedevice to a destination device, e.g., a display terminal. The cable maynot accurately convey the signals because of losses which accumulatealong the cable path. These losses are primarily due to the physicalcharacteristics of the transmission cable and sometimes due toimperfections in the cable construction. The imperfections may notnecessarily be due to manufacturing deficiencies, but may also be due tothe fact that a cable is a physical device and most physical devicesexhibit some losses when a signal is conveyed through them. Thus, longerlength transmission cables tend to exhibit more loss (also known as“cable insertion” loss) than shorter length cables. A length limitexists for each transmission cable medium after which a video signal mayno longer be discernable.

Video may be transmitted either in digital or analog format. For digitalvideo transmission such as computer video, cable insertion loss isgenerally not an issue because the digital signal can be recovered solong as discernable digital pulses are detected by a receiver. Apulse-detection method and apparatus is described, for example, incommonly owned U.S. patent application Ser. No. 11/897,547 entitled“Method and Apparatus for Improving the Quality of a Transmitted VideoSignal,” which was filed with the U.S. Patent and Trademark Office onAug. 29, 2007 and the specification of which is incorporated herein inits entirety by reference. For analog signals such as NTSC (NationalTelevision Standards Committee) video signals, the signal comprisesvarying voltages with the voltages being affected by wire length,connectors, heat, cold, materials, manufacturing processes, and/or otherconditions.

Cable insertion loss varies with the type of transmission medium. Forinstance, coaxial cables are known to exhibit less insertion loss thantwisted pair cables, thus coaxial cables are the medium of choice forvideo transmission. Also, because of its superior performance overtwisted pair cables, coaxial cables are typically used for transmissionof high resolution (i.e., broadband) video signals. However, coaxialcables are more expensive and difficult to install when compared totwisted pair cables.

Historically, the significant differences between coaxial and twistedpair cables limited twisted pair cables to transmission oflow-resolution video (i.e., less than 10 MHz) signals. However, twistedpair cables have a distinct advantage over coaxial cables, namely, thecost/performance ratio. Dollar-for-dollar, twisted pair cables aresignificantly cheaper to purchase and/or install than coaxial or fiberoptic cable. A standard twisted pair cable contains four pairs ofconductors in a single cable so that the actual cost per pair isone-quarter of the per-foot price.

Analog video specifications such as C-Video, S-Video, or YUV (or YIQ)may be available in various color models. A color model (also known as“color space”) defines colors in some standard, generally accepted way.For example, the RGB color model includes R for the red component; G forthe green component; and B for the blue component.

Data-grade twisted pair cable comes in two types: unshielded twistedpairs commonly called UTP, and STP (shielded twisted pairs). By far,most of the domestic data installations tend to employ UTP cables.

In the mid 1980's, twisted pair technology began to emerge which couldtransmit 2 Mbps (Megabits per second), then 4 Mbps (the original IBMdata rate), and then 10 Mbps. As data rates increased, it becameapparent that some means of assessing twisted pair cable performance wasneeded. It was at that time that a system of “Levels” was proposed. TheTIA (Telecommunications Industry Association)/EIA (ElectronicsIndustries Alliance), two groups that set standards for thecommunications industry, adopted the proposal and separated the datarates and other parameters into “Categories”, such as Category (CAT) 3,4, 5, and 6. Each higher numbered category has more stringentrequirements with higher data rates and higher performance than theprevious category.

The specifications for each category are given in TIA/EIA-568-B.TIA/EIA-568-B is a set of three telecommunications standards publishedby the TIA. The standards address commercial building cabling fortelecommunication products and services. The three standards areformally titled ANSI/TIA/EIA-568-B.1-2001, -B.2-2001, and -B.3-2001. TheTIA/EIA-568-B standards were first published in 2001 and supersede theTIA/EIA-568-A standards set, which is now obsolete. For example, theTIA/EIA-568-B.1-2001 defines the pin/pair assignments foreight-conductor 100-ohm balanced twisted pair cabling. These assignmentsare named T568A and T568B.

With regard to appearance, present-day twisted pair cables lookidentical to POTS (Plain Old Telephone Service) cable. The cables usethe same color code, come in many of the same pair counts and use thesame gauge conductors. However, the specifications they are made to, thematerials used to make them, and the requirements to connect them,become more and more critical as data rates increase.

The 4th pair of a CAT 5, 6, or 7 wire bundle may be used to convey powerand digital communications between a transmitter to a receiver, anddigital communications from the receiver to the transmitter. The digitalcommunications have identification bits, which identify the transmittingdevice. A number of transmitters may transmit into the samecommunication link. Collision may be detected by CRC (Cyclic RedundancyCheck) error checks.

High-resolution analog video such as RGB requires that each colorcomponent be transmitted separately to a destination device. For suchtransmission, a coaxial cable setup will require three separate coaxialcables to carry each color component and another cable to carry audiodata. In contrast, a twisted pair setup only requires one twisted paircable for all the video components, and a spare pair of conductors foraudio and other communication needs. For instance, each of the threecolor components of the RGB format video may use one out of the fourtwisted pair conductors in the cable bundle, and the last (i.e. fourth)twisted pair may be used for power and/or digital communication needs.Thus, twisted pair bundles have a clear advantage over coaxial cables interms of installation and costs.

Various methods for compensation of signal transmission errors have beenused. Specifically, methods and apparatuses to compensate for phase, DCerror, AC loss, and skew error are described, for example, in commonlyowned U.S. patent application Ser. No. 11/309,120, filed Jun. 23, 2006,and entitled “Method and Apparatus for Automatic Compensation of Skew inVideo Transmitted over Multiple Conductors,” U.S. patent applicationSer. No. 11/309,123, filed Jun. 23, 2006, and entitled “Method andApparatus for Automatic Reduction of Noise in Video Transmitted overConductors,” U.S. patent application Ser. No. 11/309,558, filed Aug. 22,2006, and entitled “Method and Apparatus for DC Restoration UsingFeedback,” U.S. patent application Ser. No. 11/557,938, filed Nov. 7,2006, and entitled “Method and Apparatus for Video Transmission overLong Distances Using Twisted Pair Cables,” and U.S. patent applicationSer. No. 11/309,122, filed Jun. 23, 2006, and entitled “Method andApparatus for Automatic Compensation of Video Signal Losses fromTransmission over Conductors,” the specifications of which areincorporated herein in their entirety by reference.

The need exists for a video format identification system which canautomatically identify the various video signal formats and switch thetransmitted video signal to the proper output connector. Such systemshould preferably be capable of simultaneously transmitting andrecovering video, audio, communication and power signals over at twistedpair cable bundle.

SUMMARY OF THE INVENTION

Some embodiments disclosed herein are generally directed to an automaticvideo format identification system.

In accordance with one aspect of the present invention, the video formatidentification system comprises a master clock circuit which providestiming and counting signals, a synchronization activity detectoroperatively coupled to the master clock circuit, and a synchronizationwidth qualifier configured to filter out noise or reference burstsignals from showing up as sync signals. The system also comprises asynchronization detector which regulates the rate of the incoming syncsignal, a color burst sampler providing a window for sampling areference color burst after the sync signal has occurred, and a colorburst detector which looks for at least three transitions from a burstsignal before it qualifies the as an appropriate reference color burst.A format sample timer generates sample clock signals. A format samplecounter produces “take format” signals which are utilized by a set offormat counter. The system further comprises a video format identifierwhich enables a particular video format to be directed to a respectivevideo connector.

These and other aspects of the invention will become apparent from areview of the accompanying drawings and the following detaileddescription of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is generally shown by way of reference to theaccompanying drawings in which:

FIG. 1 is a block diagram of a system configured for audio/videocommunication over long distances using twisted pair cable in accordancewith an embodiment of the present invention;

FIG. 2 is a schematic illustration of an exemplary allocation ofconductors of a twisted pair cable for various video formats inaccordance with an embodiment of the present invention;

FIG. 3 is a schematic illustration of another exemplary allocation ofconductors of a twisted pair cable for various video formats inaccordance with an embodiment of the present invention;

FIG. 4 depicts a DC restoration circuit in accordance with an embodimentof the present invention;

FIG. 5 shows a synchronization and reference burst detection circuitryin accordance with an embodiment of the present invention;

FIG. 6 is a flow chart of exemplary logic steps employed during videosignal format identification in accordance with an embodiment of thepresent invention;

FIG. 7 is a block diagram depicting signal switching at the receiver endin accordance with an embodiment of the present invention;

FIG. 8 is a block diagram depicting simultaneous audio, video andcommunication signal transmission in accordance with an embodiment ofthe present invention;

FIG. 9 is a block diagram depicting transmission of stereo audio andunidirectional communication signals in accordance with an embodiment ofthe present invention;

FIG. 10 is a block diagram depicting transmission of stereo audio anddirectional communication signals in accordance with an embodiment ofthe present invention;

FIG. 11 is a schematic illustration of a master clock circuit inaccordance with an embodiment of the present invention;

FIG. 12 is a schematic illustration of a sync activity detector inaccordance with an embodiment of the present invention;

FIG. 13 is a schematic illustration of a sync width qualifier circuitryin accordance with an embodiment of the present invention;

FIG. 14 schematically depicts the qualification of a sync signal inaccordance with an embodiment of the present invention;

FIG. 15 is a schematic illustration of a synchronization detector inaccordance with an embodiment of the present invention;

FIG. 16 is a schematic illustration of a color burst sampler and a colorburst detector in accordance with an embodiment of the presentinvention;

FIG. 17 is a schematic illustration of a tri-level detector inaccordance with an embodiment of the present invention;

FIG. 18 is a schematic illustration of a format sample timer and aformat sample counter in accordance with an embodiment of the presentinvention;

FIG. 19 is a schematic illustration of a format identifier in accordancewith an embodiment of the present invention;

FIG. 20 is a block diagram of a plurality of format counters inaccordance with an embodiment of the present invention;

FIG. 21 is a block diagram of a synchronization generator circuit inaccordance with an embodiment of the present invention; and

FIG. 22 is a block diagram of a synchronization signal stripper circuitin accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of illustrated exemplaryembodiments and is not intended to represent the only forms in whichthese embodiments may be constructed and/or utilized. The descriptionsets forth the functions and sequence of steps for constructing andoperating the present invention in connection with the illustratedembodiments. However, it is to be understood that the same or equivalentfunctions and/or sequences may be accomplished by different embodimentsthat are also intended to be encompassed within the spirit and scope ofthe present invention.

Some embodiments of the present invention will be described in detailwith reference to an automatic video format identification system, asgenerally depicted in reference to FIGS. 1-22. Additional embodiments,features and/or advantages of the invention will become apparent fromthe ensuing description or may be learned by practicing the invention.In the attached figures, the various drawings are not to scale with likenumerals referring to like features throughout both the drawings and thedescription.

FIG. 1 is a block diagram of a system 100 configured for audio/videocommunication over twisted pair cable in accordance with an embodimentof the present invention. In one or more embodiments of the presentinvention, audio/video communication system 100 includes a transmitter104 which is operatively coupled between an audio/video source 102 and areceiver 108. Transmitter 104 is configured to accept and process mostaudio and video formats originating from audio/video source 102 overtransmission cable bundle 103. Transmitter 104 communicates withreceiver 108 via a twisted pair cable 106.

Transmitter 104 receives video and audio signals from audio/video source102, processes the same and differentially transmits output signals overtwisted pair cable 106. Each of transmitter 104 and receiver 108 mayinclude circuits for bi-directional digital communication.Bi-directional communication may be necessary to request a resend ofdata when the transmitted data is corrupted.

Transmission cable bundle 103 may include any combination of conductorssuitable for coupling video and/or audio signals from source 102. Thevideo conductors may include, but are not limited to, VGA cables,coaxial cables, twisted pair cables and/or the like for carryingcomposite video, S-Video and high resolution computer-video. Ifconfigured as audio cables, such cables may include two high fidelityaudio conductors separately carrying the left and right audio channels.

Transmitter 104 may be configured with a composite video input on afemale BNC (bayonet Neill-Concelman) connector, an S-Video input on afemale 4-pin mini DIN, a computer-video input on a female 15-pin HD HighDefinition) connector, and audio connectors. The audio connectors may beRCA type connectors for carrying any standard audio patch cables, asneeded.

Twisted pair cable 106 may be configured as a single twisted pair cablebundle or multiple twisted pair cable bundles, depending on the desiredconfiguration of transmitter 104 and receiver 108. Multiple twisted paircable bundles may be desirable for transmission of different videoformats. For example, one twisted pair cable bundle may be used for RGBoutput while a second twisted pair cable bundle is utilized for AVoutput. The connectors on both ends of the cables may be similar, e.g.,male RJ-45 connectors to mate with female RJ-45 connectors on thetransmitter and receiver sides.

FIG. 2 is an illustration of an exemplary allocation of conductors oftwisted pair cable bundle 106 for various video formats in accordancewith an embodiment of the present invention. Each twisted pair cablebundle may include four pairs of conductors, although in otherembodiments different number of conductor pairs may be utilized.Specifically, the first conductor pair may include Pins 1 and 2; thesecond conductor pair may include Pins 4 and 5; the third conductor pairmay include Pins 7 and 8; and the fourth conductor pair may include Pins3 and 6.

The fourth pair (i.e. Pins 3 and 6), for example, may be used fordigital communication and power transfer. Power transfer may benecessary between transmitter 104 and receiver 108 when the location ofone of the devices (i.e. transmitter or receiver) is too remote from anexternal power source. In some installations, receiver 108 may belocated in close proximity to a destination device 110 (e.g. aprojector) and may have easy access to the power source used to powerdestination device 110. In such case, it may become necessary totransfer power from receiver 108 to transmitter 104, which may belocated far away from the projector power source. Destination device 110receives input from receiver 108 via transmission cable bundle 109, asgenerally shown in FIG. 1.

Conductor pairs may also be allocated as further illustrated inreference to FIG. 2 or FIG. 3, depending on video format. Note that thepin allocations used herein are for illustrative purposes andconvenience in separating the color components. For instance, with RGBvideo, the signals may be allocated such that Pins 1 and 2 carry thedifferential Red signals (i.e. Red+ and Red−), Pins 4 and 5 carry thedifferential green signals (i.e. Green+ and Green−), Pins 7 and 8 carrythe differential Blue signals (i.e. Blue+ and Blue−), and Pins 3 and 6carry Digital/Power+ and Digital/Power−, respectively.

The sync signals may be summed with the respective color components, asillustrated. For example, when the format to be transmitted is RGBHV(i.e. RGB with separate horizontal and vertical sync signals), theVertical Sync signal is summed with the Red signal (i.e. Red/V Sync+ andRed/V Sync−); and the Horizontal Sync signal is summed with the Bluesignal (i.e. Blue/H Sync+ and Blue/H Sync−). When the format to betransmitted is RGBS (i.e. RGB with one composite sync signal), thecomposite sync signal may be summed with the Blue signal (i.e. Blue/CSync+ and Blue/C Sync−).

When the format to be transmitted is RsGsBs (i.e. each color componenthas its own sync signal), the sync signals are summed with therespective color component signals, as shown in FIG. 2. When the formatto be transmitted is RGsB (i.e. only the Green color component has itsown sync signal), the differential sync signals are summed with thecorresponding green color signal, as shown in FIG. 2.

Component video signals may be allocated such that Pins 1 and 2 carrythe differential Red signals (i.e. R−Y+ and R−Y−); Pins 4 and 5 maycarry the differential luminance signals (i.e. Y+ and Y−); and Pins 7and 8 may carry the differential Blue signals (i.e. B-Y+ and B−Y. ForS-Video, the signals may be allocated such that Pins 1 and 2 are notused for video; Pins 4 and 5 may carry the differential luminancesignals (i.e. Y+ and Y−); and Pins 7 and 8 may carry the differentialChrominance signals (i.e. C+ and C−). For Composite Video, the signalsmay be allocated such that Pins 1, 2, 7, and 8 are not used; and Pins 4and 5 carry the differential video signals (i.e. Video+ and Video−).

In another embodiment of the present invention, Composite video andS-Video signals may share the same twisted pair cable, as illustrated inFIG. 3. Particularly, the composite video signals may be allocated suchthat Pins 1 and 2 carry the differential video signals (i.e. “CompositeVideo”+ and “Composite Video”−); Pins 4 and 5 carry the differentialluminance signals (i.e. Y+ and Y−); and Pins 7 and 8 carry thedifferential Chrominance signals (i.e. C+ and C−). Pins 3 and 6 carrypower and digital communication signals, as needed.

The following table illustrates which conductor pair of twisted paircable 106 may contain a synchronization (“sync”) and/or color burstsignals for a particular video format, in accordance with an exemplaryembodiment of the present invention.

Composite Composite S-Video S-Video Trans. 1 Trans. 2 Trans. 1 Trans. 2Component RGBHV RGBS RED H & V BURST H & V V (Pair1&2) BURST GREEN H & VH & V BURST H & V (Pair4&5) BURST BLUE H H & V (Pair7&8)As shown hereinabove, for RGBHV & RGBS formats, the V (Vertical) and H(Horizontal) sync signals may be added to the Red & Blue color pairs,respectively, in transmitter 104.

In the above table, “BURST” refers to a color burst signal, “Trans. 1”refers to a newer video format transmitter, and “Trans. 1” refers to anold video format (low resolution) transmitter. In composite video, thecolor burst signal is used to keep the chrominance subcarriersynchronized in a color television signal. By synchronizing anoscillator with the color burst at the beginning of each scan line, atelevision receiver can restore the suppressed carrier of thechrominance signals and decode the color information. The Composite,S-Video & Component formats are passed through (after being DC restored)to the color pairs as listed hereinabove in tabular form.

DC restoration is a common video function which is employed whenAC-coupled signals have lost their DC reference and must have itperiodically reset in order to retain brightness information. It isfairly common in video transmission systems to AC-couple the analogvideo input signal into a given device. This allows the receiving deviceto set its own optimal DC bias level independently of the drivingsignal's DC bias level. For instance, the receiving device may set theanalog signal's common mode level around V_(CC)/2 to optimize itsheadroom while processing the signal. The receiving device may alsomatch the clamped level to a DC reference voltage so as to allow forstable DC output voltage.

In one or more embodiments of the present invention, the video signal attransmitter 104 is DC restored, i.e. referenced to ground, before beingsent out to receiver 108 on twisted pair cable 106 (FIG. 1). Asgenerally depicted in FIG. 4, DC restoration circuit 112 functions bysampling the back porch of incoming video signal 114 and referencingthis signal to ground level. A clamp pulse generator 116 detects theincoming synchronization signal, whether a combined Sync-On-Green or aseparate RGB sync signal. Once the synchronization signal is detected, aclamp pulse is generated at the appropriate time to sample the backporch of the video signal. A sample-and-hold circuit 118 provides thecorrect offset voltage to summing node 120 (FIG. 4) to compensate forthe signal offset. The other voltage at summing node 120 is provided byinput capacitor 122 (FIG. 4). The resulting voltage signal is passedthrough video amplifier 124 (FIG. 4) and output amplifier 126 (FIG. 4)which restores the output signal (128) to its proper DC voltage levelwith respect to ground. Offset corrected output 128 is shown inreference to FIG. 4. In one or more embodiments, output amplifier 126(FIG. 4) may be capable of offset correction. The video signal may beadjusted in amplitude and peaking to compensate for signal transmissionloss across the length of twisted pair cable 106.

With the video signal D.C. restored at transmitter 104, the sync & colorburst signals may be detected in receiver 108 by way of voltagecomparators that are referenced to the appropriate voltage levels. Inone or more embodiments of the present invention, receiver 108 isconfigured to detect in which color pair(s) the sync & reference burstsignals may be present.

FIG. 5 schematically shows a sync and reference burst detectioncircuitry 130 utilized in accordance with the general principles of thepresent invention. The video signals, after compensation, are amplifiedand input on Red, Green and Blue as shown at reference numeral 132. Asdepicted in reference to FIG. 5, two reference level voltages areestablished; one for detecting the synchronization signals and anotherone for detecting the reference burst signals. In this regard,comparators 134, 136 and 138 are DC coupled to detect with which colorsthe sync signals are associated. Comparators 140 and 142 (FIG. 5) are ACcoupled to detect with which color the color burst signal is associated.Digital video signals 144, 146, 148, 150 and 152 (FIG. 5) are outputfrom their respective comparators to a video format identification logiccircuit configured in accordance with the present invention. Such acircuit may be implemented as a CPLD (Complex Programmable Logic Device)or FPGA (Field-Programmable Gate Array) using counters and registers. Inthe former case, the input signals to the CPLD would be G_Sync (Sync. onGreen Detection), R_Sync (Sync. on Red Detection), B_Sync (Sync. on BlueDetection), GBrst (Reference Burst on Green Detection), RBrst (ReferenceBurst on Red Detection), Tri_Lvl (Tri-Level Detection), Rst (SystemReset) and M50_Osc (50 MHz Oscillator). All the detection signals comefrom comparators which are referenced with the appropriate voltagelevels for the video signal.

To qualify the video format the video signal is analyzed extensivelyusing timing counters for width of sync signals as well as position &frequency of reference burst signals. Also tri-level sync signals aredetected, which would enable component video output in addition to thenon-tri-level component video signals.

In one or more embodiments of the present invention, the CPLD uses amaster clock circuit 200 as a source for timing and counting signals, asgenerally shown in reference to FIG. 11. For example, master clockcircuit 200 may include an oscillator 202 (FIG. 11) and a plurality ofbinary counters, in which each stage divides the previous stagefrequency in half (twice the time). In one exemplary embodiment, masterclock circuit 200 uses twenty-one (21) binary counters and a 50 MHzoscillator. A person skilled in the art would appreciate that timing iscritical in this case. HCLK signal 206 (FIG. 11) is selected toguarantee that at least one horizontal sync signal would occur betweenits rising edges. VCLK signal 208 (FIG. 11) similarly is selected toguarantee that at least one vertical sync signal will occur between itsrising edges.

In another embodiment of the present invention, the CPLD utilizes a syncactivity detector 210 (FIG. 12). Sync activity detector 210 isconfigured so that its outputs (G_ACT, B_ACT) 212 and (R_ACT) 214 wouldbe active if there are transitions between high and low levels withinappropriate time intervals. In one exemplary embodiment, the horizontalsignals may appear on Green or Blue video. These signals are monitoredfor activity using the HCLK clock. The Vertical sync signal for RGBHV isadded to the Red video signal and is qualified with the VCLK clock.Thus, if the sync is not present or the video signal is consistentlyhigh or low level, the activity signals will be inactive (low level).This condition may serve as the first qualifier for synchronizationsignals in accordance with the invention.

In yet another embodiment of the present invention, the CPLD may usesync width qualifier circuitry 216 (FIG. 13). Sync width qualifiercircuitry 216 is configured to filter out noise or a reference burstsignal from accidentally showing up as a sync signal. In one exemplaryembodiment, any signal <200 ns would disable GS_Reg output 218 (FIG.13). Conversely, any sync signal that is 200 ns or greater will clockthe GS_Reg high which would provide a second qualifier for thesynchronization signal.

FIG. 14 generally depicts the qualification of a good sync signalshowing up on the Red, Green, and/or Blue video lines. The GSync_Good,RSync_Good and BSync_Good signals (216, 218, 220) would pass thesynchronization signal if the signal is “active” and “equal to orgreater” than a pre-set minimum sync signal width, such as for example200 ns.

In still another embodiment of the present invention, the CPLD utilizesa synchronization detector 222 (FIG. 15). Synchronization detector 222is the third, and last, sync qualifier which guarantees that the syncsignal is coming in at the right rate, at least one sync within theappropriate HCLK or VCLK time. If the sync signals are not coming infast enough or are not detected at all, GDet 1 register 224 (FIG. 15)would be clocked high and the NS (No Sync On color) signal would becomeactive. Otherwise, the SO (Sync On color) signal would be active. Theseare the signals along with the reference burst signals that are used indetermining the video format.

The CPLD of the present invention may also utilize a color burst sampler226 and a color burst detector 228, as schematically depicted inreference to FIG. 16. Color burst sampler 226 provides a window forsampling a reference color burst at the appropriate time after asynchronization signal has occurred. In one exemplary embodiment, withthe event of the trailing edge of the Red or Green synchronizationsignal, CSA register 230 is clocked high enabling the CSB counter(timer) which would set (SB_Start) the Sample Burst register (CSMP) at720 to 800 ns after the trailing edge of the sync signal. This allowscolor burst detector 228 to start looking in the appropriate place forat least three transitions from the burst signal before it is qualifiedas a good Reference Burst at which time G3 register 230 (FIG. 16) isclocked high.

When the window closes, after an additional 1.3 μs (CB_Stop), the G3state is transferred to the GBD (RBD) register which qualifies a goodreference burst. The color burst sampler continues counting up to “45”(3.6 μs) before resetting color burst sampler 226 to arm the circuit forthe next sample. This allows the current reference burst to pass. Thus,the reference burst is qualified by a window at the location where areference burst is specified and also counting a number of minimumtransitions (3) to occur within that window.

The CPLD of the present invention may further utilize a tri-leveldetector 232 (FIG. 17). If a synchronization signal is Tri-level it isdefined as Component format. Component format video does not have to beTri-level, for instance it can have normal synchronization without areference burst on green and without any synchronization signal on redor blue. A positive voltage comparator is used to detect tri-levelsynchronization. A tri-level synchronization signal has a negativenormal sync followed by the signal going to a high level. In oneexemplary embodiment, since it may take some time to transition to ahigh level, the signal is not sampled until 160 ns after the trailingedge of the normal sync signal. The clock for the TRI register is takenfrom the CSB 1 time counter, as discussed in reference to FIG. 16hereinabove. This provides the 160 ns timing after the normal syncsignal.

FIG. 18 generally depicts a format sample timer 234 and a format samplecounter 236 which generate sample clocks (SAMPLE 238) and a take formatsignal 240 (TAKE 10), respectively. These signals are used by aplurality of format counters which are described herein below. In oneexemplary embodiment, format sample timer 234 (FIG. 18) generates asample clock every SCLK time (2.62 ms). Format sample counter 236 inturn provides a TAKE 10 signal (240) for every ten SAMPLE clocks (238).The sample interval ends when a counter reset signal (FCRst) becomesactive on the eleventh count, starting the sample interval over again.

The CPLD of the present invention may also utilize a format identifier242 (FIG. 19). Format identifier 242 is configured to qualify videoformats by identifying unique combinations of sync and reference burstsignals occurring on particular video color signals. A table of signalcombinations is incorporated hereinabove. The input signals come fromthe sync and color burst detectors (FIGS. 15-16). SOG, SOB, SOR signals(244, 246, 248) refer to Sync on Green, Sync on Blue and Sync on Red,respectively, while the NSOG, NSOB, NSOR signals refer to No Sync onGreen, No Sync on Blue and No Sync on Red, respectively. NSOG and NSORsignals are identified, for example, at reference numerals 250 and 252,respectively, in FIG. 19.

GBD signal 254 and RBD signal 256 refer to “reference burst signals onGreen and Red”, respectively. NGBD signal 258 and NRBD signal 260 (FIG.19) refer to “no reference burst signals on Green and Red”. While thefive (5) video formats are shown, a person skilled in the art wouldrecognize that the Component signal also is enabled with the tri-leveldetect signal.

FIG. 20 generally shows a plurality of format counters 270. Each of thefive (5) video formats has its individual counter circuit. This providesan additional filter in case a false format is detected, e.g. during aVertical sync period. In one exemplary embodiment, ten samples are takenat a rate (2.62 ms) that guarantees that at least 8 samples would betaken within the video field for good sampling. During SAMPLE time (FIG.18) if a particular video format is detected, the format counter forthat video format will count up. Once a particular counter reaches sevencounts within the ten count sample period it would declare that videoformat as a winner (WINR signal 272) and stop all counters for allformats. The TAKE 10 signal (274) would then subsequently clock thatwinners format Enable register (F#_Enbl), enabling a particular videoformat to be directed to the appropriate video connector on thereceiver. All other video output connectors would be disabled.

A u-Controller may also be employed in the video format identificationprocess in accordance with the general principles of the presentinvention. Other appropriate implementations and/or circuitconfigurations may also be utilized, as needed.

FIG. 6 shows an exemplary flow chart which represents the logic stepsemployed during video signal format identification in accordance withthe general principles of the present invention. In one or moreembodiments, the color burst occurs within a certain time period afterthe horizontal synchronization pulse. The detection of a color burst isaccomplished by sampling only during the specified period after thehorizontal sync signal has been detected. Several consecutive samplesmay be verified (tested) before changing video formats to prevent falsedetection. For example, upon starting the test, the CPLD may check forthe presence of green sync signal (step 154). If such a signal is found,the CPLD may check for the presence of red burst signal (step 156). Ifthe red burst signal is present, the detected video format is passed onto transmitter 1 (S-Video) (step 158). The remaining steps may bereadily ascertained from a review of the flow chart, as shown in FIG. 6.

After the correct video format has been identified, red, green and bluevideo signals 180 (FIG. 7) are routed to the appropriate videoconnector, such as S-Video connector 182 (FIG. 7) with all otherconnectors being made inactive. This may be accomplished by disablingamplifiers that don't follow the incoming signal format. Particularly,such amplifiers are powered down and left in a high impedance state. Inthis regard, FIG. 7 schematically shows Composite and S-Video amplifiers184 and 186, Component amplifiers 188 and RGB amplifiers 190 beingoperatively coupled to their respective connectors.

Since there are two transmitter-to-twisted pair configurations forS-Video and Composite video, there are two sets of amplifiers to enablethe correct routing of signals. For the RGBHV or RGBS video formats, thesynchronization signals are stripped from the video by disabling the RGBamplifiers during sync time. Also, separate sync signals are generatedfor the RGB video format from those embedded with the Red & Blue videosignals. In this regard, FIG. 7 shows a sync generator 192 operativelycoupled to RGB connector 194.

In one or more embodiments of the present invention, video andsynchronization signals are sent on twisted pair cable 106 (FIG. 1)differentially. For example, the red signal may be sent on pairs 1 and2, the green signal may be sent on pairs 4 and 5, and the blue signalmay be sent on pairs 7 and 8. The fourth wire pair 3 and 6 may be usedfor transmission of differential audio, communication and/or DC powersignals.

Known audio/video transmission systems limit the use of sending audioand communication signals at the same time. The following setupgenerally describes a method for transferring audio & communicationsalong with video signals without significant modification to one or moreknown audio/video transmission systems.

Adding a common mode signal on top of the existing differential videosignal to transfer additional information is useful. One limitation,however, is that the signal is susceptible to noise induced in the cablefrom external sources. Another limitation has to do with ground loopswhich degrade the common mode signal. To address these limitations andin accordance with the general principles of the present invention, twotwisted pairs may be employed to send a differential signal in whicheach one of the twisted pairs operates in a common mode configuration(i.e. Common Mode/Differential or CMD), as generally shown in referenceto FIG. 8.

For example, if twisted pair 1 and 2 sends the Audio+signal (FIG. 8) ina common mode configuration, while twisted pair 4 and 5 sends theAudio−signal (FIG. 8) in a common mode configuration, a differentialsignal is achieved between the pairs. A person skilled in the art wouldreadily appreciate that the use of two twisted pairs in a CMDconfiguration has advantages over the use of a single common modesignal. Specifically, it reduces noise induced in the signal beingtransmitted, which would be generated by an external source. A secondadvantage would be enhanced noise immunity due to ground loops.Moreover, video, audio, and communication signals may be sentsimultaneously using only one twisted pair cable (e.g., CAT 5).Particularly, video and sync signals may be sent differentially ontwisted pairs 1 and 2, 4 and 5, and 7 and 8. Mono-Audio may be sent (ina CMD configuration) over twisted pairs 1 and 2 and 4 and 5.Bi-directional communication signals may be sent on the remaining fourthwire pair.

In one or more embodiments of the present invention, communicationsignals are transferred on the fourth wire pair using a Master/Slaveconfiguration. The Master (Transmitter) has a built in state machinewhich may be configured, for example, to sample the source signal (i.e.,a RS232 port) every 5 μsec. and drive the fourth wire pair with an LVDS(Low Voltage Differential Signal) transceiver after which it would turnoff the line driver. After the Master transmits its information it willlisten for a response from the Slave (Receiver). When placed inBi-Directional mode the Slave (Receiver) also has a state machine thatwaits for the pulse from the Master, after which it turns the linearound and enables its LVDS line driver and sends the state of itssource signal. If the Slave (Receiver) is placed in unidirectional modeit will only receive data from the Master and not respond (i.e., notdrive the fourth wire pair back from its end). When the Slave does notrespond the Master's RS232 output is left in the idle (Mark) state.

If the source (RS232 port) is in the Mark (1) state, the unit may beconfigured to send a 400 ns wide pulse. If the source is in the Space(0) state, the unit would send a 100 ns wide pulse. In Bi-directionalmode the Transmitter & Receiver are continuously sending back and fourththese pulses every 5 μsec. If the Receiver is placed in unidirectionalmode, the Transmitter would send pulses every 5 μsec. Thus in thisexample, the frequency content of the pulses would be >1 MHz, i.e. arelatively high frequency compared to audio which is transmitted in the20-20 KHz range.

In accordance with an alternative embodiment of the present invention,in cases when only unidirectional communication is required, theaddition of differential amplifiers to the fourth wire pair would allowa second CMD channel to be implemented on twisted wire pairs 7 and 8 and3 and 6. The first CMD channel would send the Right Audio source whilethe second CMD channel would send the Left Audio source. The second CMDchannel configuration is schematically shown in reference to FIG. 9.

In accordance with another alternative embodiment of the presentinvention, in cases when bidirectional communication is required, theaddition of high pass and low pass filters to the fourth wire pair wouldallow the second CMD channel to be implemented. The first CMD channelwould send the Right Audio source while the second CMD channel wouldsend the Left Audio source. The second CMD channel configuration isschematically shown in reference to FIG. 10.

If only Mono-Audio is required for twisted pairs 1 and 2 and 4 and 5,power signals may be sent on the fourth twisted wire pair along the lowpass filter route (FIG. 10). Thus, video, audio, bidirectionalcommunications and power could be efficiently sent on a single CAT 5cable.

One or more embodiments of the invention are also concerned withautomatically stripping synchronization signals for RGB video formatsfrom the Red (Vertical) and Blue (Horizontal) twisted pair signals asdesigned within the CPLD of the present invention. Other embodimentsdeal with generating separate synchronization signals when detecting RGBvideo format.

With the RGB video format, transmitter 104 (FIG. 1) takes the separatesynchronization signals and passes the same through a unipolarconverter, which converts these signals to a positive polarity. Theuni-polar sync signals are then subtracted from the video signals, withthe red pair having the vertical sync signal and the blue pair havingthe horizontal sync signal for the RGBHV video format. If the videoformat is RGBS then the synchronization signal would be on the blue paironly, as shown in tabular form hereinabove.

In one embodiment, the input signals to the CPLD are R_Sync (Sync. onRed Detection), B_Sync (Sync. on Blue Detection), M50_Osc (50 MHzOscillator), the FMT4 (RGBS detect), FMT7 (RGBHV detect), HPOL(Horizontal sync Polarity) and VPOL (Vertical sync Polarity). All thedetection signals, R_Sync and B_Sync, come from comparators which arereferenced with the appropriate voltage levels for the video signal.

FIG. 21 schematically depicts a synchronization generator circuit 300.If an RGBHV video format (FMT7 signal 302) is detected, both theHorizontal sync (BSYNC signal 304) and the Vertical sync (RSYNC signal306) are enabled to go through the polarity converter to be delivered tothe Horizontal and Vertical synchronization pins of the VGA connector.If RGBS video format (FMT4 signal 308) is detected, only the combinedsync (BSYNC) is enabled to go through the polarity converter and to bedelivered to the Horizontal synchronization pin of the VGA connector.The polarity converter is an exclusive-OR gate in which if the HPOL(310) or VPOL (312) is at high level, the corresponding synchronizationsignal will be inverted. Otherwise if HPOL (310) or VPOL (312) is low,the synchronization signal is not inverted. Some video formats requireone or both synchronization signals to be inverted.

FIG. 22 schematically depicts a synchronization signal stripper circuit400. Since synchronization signals are added to the Red and Blue videoon twisted pair cable 106 (FIG. 1) for RGBHV video format, it isnecessary to remove these signals from the video before delivery to theVGA video connector. The generation of separate synchronization signalstakes place before the stripping of synchronization signals.Conventional setups use the synchronization signals themselves to stripthe sync signals from the video. This practice leaves a remnant of thesync signal on the video because there is a slight delay betweendetecting a sync signal and subsequently removing the sync from thevideo.

For RGBHV signal format and in accordance with the general principles ofthe present invention, it may be desirable to measure the distancebetween and location of prior synchronization signals in order to removecurrent synchronization signals ahead of their occurrence, thuseliminating the remnant of sync in the video signal. In one exemplaryembodiment, an 11-bit binary up-counter 402 and an 11-bit binary downcounter 404 are utilized. There are two identical circuits in thepresent configuration. For simplicity, a description of horizontal syncstripping from the blue video signal follows.

When the leading edge of a sync signal (BSYNC) is detected the DET1register will be clocked high with a clock (50 MHz). This would clock asecond register (LD1) which loads the down-counter with the value in theup-counter, which has counted the time interval between synchronizationsignals. On the next 50 MHz clock, the reset register (RST1) will resetthe up-counter and turn off the load signal to the down-counter. On thenext negative transition of the 50 MHz clock, the reset register willbecome inactive. At that point, the up-counter begins to count theinterval taken between the current and the next sync signal. Thedown-counter is counting down the time taken by the previous intervalbetween the sync signals.

When the down counter reaches a count of five (5), strip register 406(STP1) would be set active (STB), causing the video to be turned off orgrounded ahead to the current synchronization signal, thus stripping thesync from the video. The video signal is turned back on after the syncsignal has passed via DET1 register 408 (FIG. 22) going low and the STP1register 406 being clocked low. An exemplary timing diagram is providedin reference to FIG. 22 to show the signal sequence.

As mentioned hereinabove, a duplicate circuit is used to remove thevertical sync (STRIP_R) from the red video signal. The difference being,that instead of counting with a 50 MHz clock, the timing interval iscounted with the number of horizontal sync signals (BSYNC) betweenvertical sync signals (RSYNC). Also, instead of starting the strip on acount of five (5), the strip is started at a count of one (1) before thevertical sync occurs.

The exemplary embodiments described hereinabove are merely illustrativeof the general principles of the present invention. Various designmodifications may be employed that would reside within the scope of theinvention. Thus, by way of example, but not of limitation, variousalternative configurations may be utilized in accordance with theteachings herein. Accordingly, the drawings and description areillustrative and not meant to be a limitation thereof.

Moreover, all terms should be interpreted in the broadest possiblemanner consistent with the context. In particular, the terms “comprises”and “comprising” should be interpreted as referring to elements,components, or steps in a non-exclusive manner, indicating that thereferenced elements, components, or steps may be present, or utilized,or combined with other elements, components, or steps that are notexpressly referenced. Thus, it is intended that the invention cover allembodiments and variations thereof as long as such embodiments andvariations come within the scope of the appended claims and theirequivalents.

1. A video format identification system for identifying a video formatof a received video signal from a plurality of possible video formatscomprising a plurality of component video signals, comprising:synchronization and reference burst signal detection circuitryconfigured to detect synchronization and reference burst signals in saidplurality of component video signals; video format identificationcircuitry operatively coupled to said synchronization and referenceburst signal detection circuitry configured to identify a format of saidvideo signal dependent on a detected presence of said synchronizationand reference burst signals in one or more of said component videosignals; video signal routing circuitry coupled to respective outputconnectors and configured to receive said component video signals andautomatically route said component video signals to an appropriate oneor more of said output connectors depending on said format of said videosignal identified by said video format identification circuitry; aninput connector for connecting to a multi-pair cable, said inputconnector comprising pins for connecting to a plurality of cable pairsof said multi-pair cable; wherein said video format identificationcircuitry is configured to identify each cable pair of said multi-paircable that contains a synchronization signal.
 2. The video formatidentification system of claim 1 wherein said video formatidentification circuitry is configured to identify each cable pair ofsaid multi-pair cable that contains a reference burst signal.
 3. Thevideo format identification system of claim 2 wherein said video formatidentification circuitry is configured to identify said format of saidvideo signal from an identity of each cable pair of said multi-paircable that contains a synchronization signal and an identity of eachcable pair of said multi-pair cable that contains a reference burstsignal.
 4. The video format identification system of claim 3 whereinsaid multi-pair cable comprises a plurality of twisted pairs.
 5. Thevideo format identification system of claim 4 wherein said multi-paircable comprises four twisted pairs.
 6. The video format identificationsystem of claim 1, wherein said video format identification circuitrycomprises logic circuitry configured to identify said format of saidvideo signal.
 7. The video format identification system of claim 6,wherein said logic circuitry comprises a Complex Programmable LogicDevice (CPLD).
 8. A method for identifying a format of a video signalfrom a plurality of possible formats comprising the steps of:transmitting a video signal comprising a plurality of component videosignals over a multi-pair cable, at least one of said component videosignals comprising a synchronization signal and at least one of saidcomponent video signals comprising a reference burst signal, each ofsaid component video signals being transmitted over a respective pair ofsaid multi-pair cable, said multi-pair cable comprising a plurality oftwisted pairs; receiving said plurality of component video signals;identifying each of said plurality of component video signals thatcomprises a synchronization signal; identifying each of said pluralityof component video signals that comprises a reference burst signal;identifying said format of said video signal from an identity of each ofsaid plurality of component video signals that comprises asynchronization signal and an identity of each of said plurality ofcomponent video signals that comprises a reference burst signal; routingsaid video signal to one or more output connectors depending on saididentified format of said video signal.
 9. The method of claim 8 furthercomprising the step of adding a reference burst signal to at least oneof said video component signals prior to transmitting said video signal.10. The method of claim 8 further comprising the step of adding asynchronization signal to at least one of said video component signalsprior to transmitting said video signal.
 11. The method of claim 8further comprising the step of removing a synchronization signal from atleast one of said video component signals prior to routing said videosignal to said one or more output connectors.
 12. The method of claim 8further comprising the step of removing a reference burst signal from atleast one of said video component signals prior to routing said videosignal to said one or more output connectors.
 13. The method of claim 8wherein said video component signals comprise a red component signal, agreen component signal, and a blue component signal.
 14. The method ofclaim 8 wherein said video component signals comprise a chrominancecomponent signal and a luminance component signal.